"Fins" (aka "backs") are only about an inch long. Does NOT self-clean, period.

Review:

I bought this barrel not because of the rifling which I'm skeptical does anything but because of the stated quality of construction. I have to give Hammerhead kudos on that - this is a well machined barrel kit and extremely lightweight.

Testing
I ran over 2000 paintballs through it ranging from X-ball bronze (500), X-ball Silver (500), and Draxxus Hellfire (1000).

First off, I also several other barrels to compare - primarily a 14" unported PPS Brass barrel - the OpsGear Interceptor 18" and the stock SP-8 14" ported barrel.

With more consistent paint like Hellfire, there are less "zingers" - paint going off at an angle. This is regardless of barrel.

No question, the Hammerhead is more accurate than the stock barrel - significantly so. What I was surprised to find was that it is NOT more accurate than the very well made PPS Brass, unported one-piece barrel. I saw *slightly* more consistency with the PPS brass, at all ranges out to about 150', the length of my indoor field.

Paint Breakage
A barrel break in the Hammerhead is where things go way downhill. It seems like one barrel break will lead to another and the barrel just doesn't self-clean. No matter how much you try to shoot through the break (I probably took 20-30 shots after the break) accuracy and consistency suffers greatly.

Breaking low-end paint had a lessor effect - it seemed to clean easier probably on account of a thinner fill.

CAUTION: If you break Hellfire which has a THICK, waxy fill, it seemed like you had to take the barrel off to clean it as it really stuck to the inside of the barrel. (likely the rifling grooves)

Rifling
There's a lot of talk about how rifling affects a paintball.
I won't make arguements for or against it but I will make a statement for consideration:

The APEX and flatline barrels cause a paintball to spin which has a clear effect on the flight path. It's a different spin in those cases (back, side or top-spin) versus rifling.

I don't know if longitudinal spin (rifling) does anything to stabilize a paintball but I would suggest the Hammerhead barrel is at least a well machined barrel which results in very-good to excellent accuracy.

"Fins" (Backs)
One thing about the Hammerhead system is the "fins" (aka: "backs) are extremely small. There's perhaps 1-2 inches of effective "back" with the rest being "front". In comparison, a Freak kit insert is about 6 inches long. I don't know how relevant this is but there are a lot of good barrel kits (two piece or inserts) that make use of a much larger "sizing" section (eg: the part you match bore with your paint). I don't know if this affects anything but it's a visible difference I felt worth mentioning. More research would be needed to determine if this has any bearing on performance.

Conclusion:

I wish I could recommend this barrel but my results just don't justify it. Usual disclaimer: there are a vast number of factors that affect how paintball equipment performs - air pressure, dwell settings, rate of fire, paint type and freshness, atmospheric conditions (temperature, humidity) and user error.

My results are from informal testing with a freshly cleaned and greased and otherwise well-shooting marker, indoors, with fresh, high-quality paint of different types.

Even if the cost was lower, the lack of effective self-cleaning makes this a challenging barrel to use on field. If you break with a tourney grade paint like Hellfire which has a snot-like fill, God help you. Sorry guys - I know a lot of people love this barrel but, taking into account breaks, I just didn't have great results with it. :(

For accuracy with a clean barrel, I'd give the Hammerhead a 9/10.

Shooting through breaks it gets a 1/10 - it just won't.

Price: very high. I don't think you can buy a more expensive kit. 1/10.

Palmer Pursuit Shop brass is more consistent, less expensive and less hassle, having no inserts or backs to change.

I have to give the HammerHead "slightly above average" (6/10) on account of very good accuracy, way too high price, inability to self-clean and availability of other options.